The present invention relates to panels consisting mainly of an insulating material such as a felt of fibres bonded together, one of the surfaces of each panel having a covering suitable in particular for receiving at least one layer of an impervious material which is resistant to weathering.
Panels of this type are already known, in particular for roofs having a slight slope, to serve both as insulating material and as support for impervious coverings, in particular of a bitumenous material.
Some known panels comprise a felt of mineral fibres bonded together having sufficient density to confer considerable rigidity on the panel while maintaining satisfactory insulating properties, and a covering consisting of a layer of glass fibres impregnated with bitumen and, on the external surface, a sheet of craft paper.
Such panels have, however, various disadvantages, such as the fact that the bond between the felt and the impervious coverings subsequently deposited on the panels after assembly lacks homogeneity due to the interposition of the sheet of craft paper and due to its sensitivity to moisture.
There has also been disclosed, in particular in U.S. Pat. No. 3,922,425 and French Pat. No. 2,025,428, a panel comprising a mineral fibre felt, one or more than one surface of which is impregnated with bitumen and covered with a thin skin of a separating agent such as a thermoplastic material which is capable of being eliminated, entirely or in part, by being torn off or by melting, combustion or dissolving in the molten bitumen used for the final impervious coverings. Such a thermoplastic material is preferably chosen from the group comprising polyethylenes and polypropylenes of low or medium density and is preferably used in the form of a sheet having a thickness of the order of 10 microns.
Such panels have, however, certain disadvantages relating both to the process proposed for their manufacture and to their properties, in particular those properties specifically conferred on them by the said process.
According to the Patents cited above, and more particularly to French Pat. No. 2,025,428, impregnation of the felt of mineral fibres is carried out by pouring a thin, continuous stream of molten bitumen over the felt from the slot of a coating apparatus. The penetration of bitumen is a function of various factors, in particular the quantity present per unit surface area, the fluidity of the product and hence also its temperature, the porosity of the felt, its own temperature, etc. Considerable heterogeneity therefore generally exists. Thus the surface layer, which is formed by a mixture of the usual type of insulating fibres and of chopped textile filaments, may be only partly impregnated or it may, on the contrary, represent only a small portion of the region of panel which has been impregnated. The finished product is therefore heterogeneous in its properties, in particular in its insulating properties, imperviousness, mechanical resistance, capacity to be bonded, etc.
Concerning the process proposed by said French Patent, it should be noted that it poses delicate problems in its execution as regards the precision of dosing, both in space and in time.
Such problems in fact arise even in the manufacture of the felt itself since in order to obtain a reinforced upper layer it is necessary to ensure homogeneous distribution of the chopped fibres introduced therein. Problems of dosing and distribution again arise subsequently at the stage of impregnation of the felt with bitumen, due to the numerous parameters which enter into this process, as mentioned above.
Furthermore, since bitumen is a very soiling product, its direct distribution over the rigid felt travelling underneath the coating slot does not enable the lateral surfaces of the felt to be correctly impregnated without risk of soiling the conveyor apparatus. All the more so is it impossible to envisage impregnating the lower edges by direct application of the process described.